The present invention relates to a residual-current circuit breaker.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Residual-current circuit breakers are provided for the protection of living beings and installations from hazardous fault currents and according to relevant international, national and regional regulations must trip upon the occurrence of a fault current which lies between half the rated fault current and the rated fault current.
In accordance with relevant international, national and regional regulations, residual-current circuit breakers must further include a testing device for testing the proper function of fault current tripping. Such a testing device usually has a test resistor and a test button, with a test current circuit being closed upon actuating the test button and, in this way, a simulated fault current being generated from one conductor to another conductor past a summation current transformer. If the residual-current circuit breaker works correctly, it is tripped and the break contacts of the residual-current circuit breaker will disconnect the conductor of a network to be protected.
In accordance with the regulations, the linkage in the summation current transformer caused by the actuation of the testing device must be smaller than 2.5 times the linkage generated by the rated fault current. In accordance with regulations, up to 75 mA are allowed to flow in the rated voltage in a residual-current circuit breaker with a rated fault current of 30 mA. A residual-current circuit breaker that trips upon actuation will therefore not necessarily trip securely even on the occurrence of a substantially lower actual full current.
The test circuit must further reliably work over a wide range of supply voltages. The test circuit must still work at supply voltages of 85% of the rated voltage, and under the usual fluctuations of the supply or network voltage of 10%. Furthermore, there are four-pole residual-current circuit breakers which may also be used as two-pole residual-current circuit breakers. This means that the simulated fault current is increased by 225% in the maximum permissible supply voltage in a test circuit which is dimensioned in such a way that the fault current simulated by the same corresponds to the rated fault current at 85% of the rated voltage. A residual-current circuit breaker which is considered to be functionally reliable at such a high simulated fault current therefore possibly presents a hazard to living beings and installations because it is not possible to securely conclude the function of the residual-current circuit breaker at the rated fault current.
It would therefore be desirable and advantageous to provide an improved residual-current circuit breaker which obviates prior art shortcomings and with which a functionality of fault current tripping can be verified more precisely in a simple and reliable manner.